Inerting methods for high altitude training, storing food or for minimizing the risk of fire in an enclosed room are generally known from inertization technology. In such inerting methods, the atmosphere of the enclosed room is usually lowered to and then maintained at an inerting level below the oxygen concentration of the ambient air atmosphere by the introduction of an oxygen-displacing gas from an inert gas source.
The preventative effect resulting from this method is based on the principle of oxygen displacement. As is known, normal ambient air consists of approximately 21% oxygen by volume, 78% nitrogen by volume and 1% by volume of other gases. In order to minimize the risk of a fire breaking out or respectively to extinguish a fire that has already broken out in an enclosed room, or to extend the shelf life of stored food, the concentration of nitrogen in the respective room is increased, and the oxygen content thus reduced, for example by introducing pure nitrogen as inert gas. An appreciable protective effect and/or fire prevention effect is known to begin once the percentage of oxygen drops below about 15% by volume. Depending upon the flammable materials (fire load) within the relevant room, it may be necessary to further lower the oxygen content to, for example, 12% by volume. Most combustible materials can no longer ignite or burn at such an oxygen concentration.
An oxygen reducing system is generally configured such that one or more defined drawdown levels can be set in the spatial atmosphere of an enclosed room within a specific amount of time and maintained for a defined period or continuously. It is thus for example necessary to rapidly reduce the oxygen content in the room's atmosphere in the event of fire so as to extinguish (quench) the fire and effectively prevent re-igniting of the material in the room at least for the duration of a so-called reignition phase.
The reignition phase noted above indicates the period of time following the so-called “firefighting phase” during which the oxygen concentration in the enclosed room is not allowed to exceed a specific value, the so-called “reignition prevention value phase,” so as to prevent the material in the protected area from reigniting. The reignition prevention level is thereby an oxygen concentration contingent upon the fire load of the room and determined by testing.
In order to be able to ensure fire prevention and/or long shelf life of stored food, the oxygen reducing system needs to be configured accordingly; i.e. it needs to be able to supply a specific volumetric flow of oxygen-displacing gases for a longer period of time. The amount of oxygen-displacing gases to be supplied per unit of time by the oxygen reducing system in an individual case depends in particular on the spatial volume and the airtightness of the enclosed room. The oxygen reducing system thus needs to have a larger capacity when the enclosed room is for example a stockroom of relatively large spatial volume since a greater volume of oxygen-displacing gases is introduced into the spatial atmosphere of the stockroom per unit of time—compared to a relatively small protected area—so as to be able to set a drawdown level within a specified period of time. On the other hand, the amount of oxygen-displacing gases supplied by the oxygen reducing system also increases per unit of time the lower the airtightness of the enclosed room is, or the higher the air exchange rate is respectively.
The influence of the spatial volume generally poses no difficulties to the configuring of an oxygen reducing system. This is due to the fact of it being relatively easy to determine the maximum spatial volume of a room equipped or to be equipped with an oxygen reducing system to be factored in and at least this spatial volume being unable to increase over time. However, it is a different matter with respect to the airtightness of the room. The air exchange rate, expressed as the so-called n50 value, is usually used as the measure of a room's airtightness.
The n50 air exchange rate is derived from the volumetric air flow per hour, when a pressure differential of 50 Pa is to be maintained, divided by the volume of the structure. Hence, the enclosed room has a higher airtightness value the lower the air exchange rate is.
A differential pressure measuring procedure (blower-door method) is usually used to measure the n50 value being a measure of a room's airtightness. However, performing a series of differential pressure measurements to determine the n50 air exchange rate is often coupled with various difficulties and requires a great deal of technical effort, particularly in larger buildings or spaces. Even when a differential pressure measurement identifies the n50 value of the respective space, this does not rule out the enclosed room's state changing over time, particularly its air exchange rate. It is thus for example conceivable for initially sealed openings in the room to become untight. Also placing objects and/or goods into the enclosed room (particularly in the case of a stockroom) impacts the air exchange rate determined by the differential pressure measurement.
The fact that the airtightness of an enclosed room not only can change over time but can also in particular worsen poses a problem when configuring oxygen reducing systems. In particular, it has not been possible to date, or only possible with great effort, to determine the airtightness of a room already equipped with an oxygen reducing system at a later point in time in order to adapt the capacity of the oxygen reducing system as needed; i.e. for example to increase the volume of oxygen-displacing gases the oxygen reducing system supplies per unit of time so as to still provide fire prevention and/or long shelf life after a decrease in the airtightness of the enclosed room.
Continuous monitoring of the airtightness of a space equipped with an oxygen reducing system is also desirable to the extent of the conclusions which might also be drawn to neighboring spaces with respect to leakages which have newly arisen. The risk in this is that oxygen-displacing gases may end up in the neighboring spaces through such newly developed leakages, which in certain circumstances might result in endangering the health of people within the neighboring spaces.